1. Field of the Invention
The present invention relates to antiscalants for reverse osmosis plants, and particularly to a polyzwitterionic acid (PZA) antiscalant compound used to inhibit the formation of scale, particularly calcium sulfate (CaSO4) scale.
2. Description of the Related Art
Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane. This membrane-technology is not properly a filtration method. In RO, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential, a thermodynamic parameter. RO can remove many types of molecules and ions from solutions and is used in both industrial processes and in producing potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be selective, this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely. RO is commonly used in desalination plants. In the reverse osmosis desalination process, the feed water splits into product water and reject brine streams. The dissolved salts in the feed water are concentrated in the reject brine stream. If supersaturation occurs and their solubility limits are exceeded, precipitation or scaling will occur.
The deposits commonly encountered in the desalination process include mineral scales (e.g., CaCO3, CaSO4 and Mg(OH)2), corrosion products, polymeric silica and suspended matter. The specific mechanism of inhibition of scaling is sequestration, or the capability of forming stable complexes with polyvalent cations. The antiscalant-treated solutions are stabilized via alteration in crystal morphology at the time of nucleation and subsequent inhibition in growth rate. Commonly used antiscalants are derived from three chemical families: condensed poly(phosphate)s, organophosphates, and polyelectrolytes. The anionic form of the antiscalants helps prevent scale formation by sequestering the cations.
Due to the extraordinary chelating properties of compounds containing aminomethylphosphonic acid groups in the molecule, it would be desirable to use such a compound for the synthesis of low molecular-weight chelating agents containing these functional groups, allowing for the formation of polymer-heavy metal ion complexes from wastewater. Further, present antiscalants typically have a relatively high phosphorous content, which is damaging to the environment. It would be further desirable to produce an effective antiscalant with a low phosphorous content.
Thus, a polyzwitterionic acid antiscalant compound solving the aforementioned problems is desired.